This proposal seeks a FIRST award to support a five-year study of discrimination learning in mentally retarded individuals. The research will make use of a programmed method for generating one-trial discrimination learning (OTDL). Successful completion of the OTDL program establishes the following two-trial performance: On the first trial, a single visual stimulus Is displayed and Its selection is reinforced. On the second trial, two stimuli are displayed, one from the previous trial and a different stimulus: selection of the previously displayed stimulus is defined as correct. Different stimuli appear on each two-trial problem. Consistently accurate performance on the second trial of each problem demonstrates acquisition of new discriminations after exposure to a single training trial. The proposed studies will apply the programmed OTDL method to several areas of interest in the analysis and remediation of learning problems in mental retardation. The specific aims are: (1) To compare the effects of programmed instruction and verbal instruction on several characteristics of the OTDL performance. By including subjects across a range of mental retardation, the comparisons will test the prediction that acquisition of such performance in lower-functioning subjects will be more successful with programmed procedures, and that higher-functioning subjects will learn equally well with either procedure. Subsequent exposure to changes in reinforcement contingencies will examine reported differences in "contingency shaped" and "rule governed" behavior. (2) To develop broadly applicable procedures for studying "breadth of attention" in mentally retarded individuals. including those classified as severely retarded. Breadth of attention refers to discrimination of the individual elements of complex stimuli after very limited exposure (e.g., a single trial) to each complex. The studies will (a) examine effects of training history on element discrimination, (b) examine for the first time breadth of attention in low-functioning mentally retarded individuals, and (c) determine whether attention can be broadened by extension of the programmed methods. (3) To determine if one-trial learning can be extended to conditional discrimination in the arbitrary matching-to-sample format. The study will investigate conditions under which a single exposure to a two-element complex will lead to selection of one element conditionally upon the other. (4) To determine if one-trial learning can be extended to the formation of classes of equivalent stimuli. The study will ask if conditional relations established in one trial are also relations of equivalence, according to widely accepted criteria established by Sidman & Tailby (1982).